In active matrix display devices, a thin-film transistor (TFT) is used as a switching element of a pixel. A thin-film transistor is also used as a switching element of a driver formed in a frame area (non-display area) outside an active area (display area).
The thin-film transistor includes a semiconductor layer. When light is incident on the semiconductor layer, light leakage current is produced. The light leakage current may decrease the contrast, and the performance of the display device may be deteriorated. To suppress such performance deterioration of the display device by the light leakage current, there is a well-known technique of forming a light shielding layer on an array substrate.
Furthermore, a light shielding layer in a floating state causes a back gate effect on a thin-film transistor. To suppress the back gate effect, there is a well-known technique of electrically connecting the light shielding layer to other components.